#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<ctype.h>
#include<fcntl.h>

#define LEFT "["
#define RIGHT "]"
#define LABLE "#"
#define DELIM "\t"
#define LINE_SIZE 1024
#define ARGC_SIZE 32
#define EXIT_CODE 44

#define NONE -1
#define IN_ROIR 0
#define OUT_RDIR 1
#define APPEND_RDIR 2

int quit=0;
int lastcode=0;
extern char **environ;
char commandline[LINE_SIZE];
char *argv[ARGC_SIZE];
char pwd[LINE_SIZE];
char *rdirfilename = NULL;
int rdir=NONE;

char myenv[LINE_SIZE];

const  char* getusername()
{
    return getenv("USER");
}

const char*gethostname()
{
    return getenv("HOSTNAME");
}

void getpwd()
{
    getcwd(pwd,sizeof(pwd));
}

void check_redir(char *cmd)
{
    char *pos=cmd;
    while(*pos)
    {
        if(*pos == '>')
        {
          if(*(pos+1) == '>')
          {
            *pos++='\0';
            *pos++='\0';
            while(isspace(*pos))pos++;
            rdirfilename = pos;
            rdir=APPEND_RDIR;
            break;
           }
          else{
              *pos='\0';
              pos++;
              while(isspace(*pos))pos++;
              rdirfilename=pos;
              rdir=OUT_RDIR;
          }
        }
        else if(*pos=='<'){
         *pos='\0';
         while(isspace(*pos))pos++;
         rdirfilename=pos;
         rdir=IN_ROIR;
        }
        else{

        }
        pos++;
    }
}

void interact(char *cline,int size)
{
    getpwd();
    printf(LEFT"%s@%s %s""RIGHT""LABLE"" ",getusername(),gethostname(),pwd);
    char *s=fgets(cline,size,stdin);
    assert(s);
    (void)s;
    cline[strlen(cline)-1]='\0';
    check_redir(cline);
}

int splitstring(char cline[],char*_argv[])
{
    int i=0;
    argv[i++]=strtok(cline,DELIM);
    while(_argv[i++]==strtok(NULL,DELIM));
    return i-1;
}

void NormalExcute(char *_argv[])
{
    
    pid_t id=fork();
    if(id<0)
    {
        perror("fork");
        return;
    }
    else if(id==0)
    {
        int fd=0;
        if(rdir==IN_ROIR)
        {
            fd=open(rdirfilename,O_RDONLY);
            dup2(fd,0);
        }
        else if(rdir==OUT_RDIR)
        {
            fd=open(rdirfilename,O_CREAT|O_WRONLY|O_TRUNC,0666);
            dup2(fd,1);
        }
        else if(rdir==APPEND_RDIR)
        {
            fd=open(rdirfilename,O_CREAT|O_WRONLY|O_APPEND,0666);
            dup2(fd,1);
        }
        execvp(_argv[0],_argv);
        exit(EXIT_CODE);
    }
    else 
    {
        int status=0;
        pid_t rid=waitpid(id,&status,0);
        if(rid==id)
        {
            lastcode=WEXITSTATUS(status);
        }
    }
}

int buildcommand(char*_argv[],int _argc)
{
    if(_argc==2&&strcmp(_argv[0],"cd")==0)
    {
        chdir(argv[1]);
        getpwd();
        sprintf(getenv("PWD"),"%s",pwd);
        return 1;
    }
    else if(_argc==2&&strcmp(_argv[0],"export")==0)
    {
        strcpy(myenv,_argv[1]);
        putenv(myenv);
        return 1;
    }
    else if(_argc==2&&strcmp(_argv[0],"echo")==0)
    {
        if(strcmp(_argv[1],"$?")==0)
        {
            printf("%d\n",lastcode);
            lastcode=0;
        }
        else if(*_argv[1]=='$')
        {
            char *val=getenv(_argv[1]+1);
            if(val)printf("%s\n",val);
        }
        else 
        {
            printf("%s\n",_argv[1]);
        }
        return 1;

     }
    if(strcmp(_argv[0],"ls")==0)
    {
        _argv[_argc++]= "--color";
        _argv[_argc]=NULL;
    }
    return 0;
}
int main()
{
    while(!quit)
    {
        //1.
        //2.交互问题，获取命令行
        interact(commandline,sizeof(commandline));

        //3. 子串分割，解析命令行
        int argc=splitstring(commandline,argv);
        if(argc==0)continue;

        //4. 指令的判断
        int n=buildcommand(argv,argc);

        //5. 普通命令的执行
        if(!n) NormalExcute(argv);
    }
    return 0;
}
